Nanotubes have been proposed as targeted drug delivery nanocapsules which may realize the "magic bullet" concept and promise many advantages over current procedures. The question arises as to whether a nanotube drug carrier could be engineered so that it is energetically favourable for the drug molecule to be encapsulated, and then once inside the cell, energetically favourable to be ejected. In other words, we need to understand and accurately predict the uptake and expulsion capacities of a particular carbon nanotube in association with the molecules of a particular drug. In this paper, for a carbon nanotube carrier, the concepts of an acceptance condition and the suction energy are used to determine the suction behaviour of cisplatin, a platinum-based anticancer drug. It is shown theoretically using elementary mechanics and applied mathematical modelling techniques that for cisplatin to be accepted, the carbon nanotube must have a radius of at least 4.785 angstrom, and that the maximum suction energy occurs when the carbon nanotube radius is 5.27 angstrom @ 2007 Elsevier B.V. All rights reserved.